The present invention relates to combustion modified isocyanate compositions useful for the production of polyurethanes for structural applications, particularly polyurethanes produced by a RIM process.
As polyurethanes increase in importance for construction applications, the importance of decreased flammability and smoke generation also increases.
Many attempts to improve the flammability characteristics of structural polyurethane foams have been made. In U.S. Pat. No. 4,221,874, for example, it is noted that many additives and modifiers have been used in an effort to decrease the rate of burning and flame spread. Most of these additives and modifiers are, however, organic materials which will also burn. The known inorganic flame retardants must generally be used in such large quantities that they have a detrimental effect upon the polymer's physical properties. U.S. Pat. No. 4,221,874 teaches that these difficulties may be overcome by including 5-50 wt. % of a brominated phospholane oxide in the organic polymer. The brominated phospholane oxide may be added to the already-formed polymer or it may be included in one of the components from which the polymer is formed.
U.S. Pat. No. 4,409,341 is also directed to improving the fire resistance of polyurethane foams. The improvement therein is said to be achieved by including 0.35-3.0 wt. % of a phosphorus compound that is liquid at room temperature in the polyol component of a polyurethane-forming system.
Brominated diphenylethers have also been incorporated in the polyol component of polyurethane forming systems in an effort to improve the flame resistance of the product polyurethane. However, the burn properties of foams produced from such polyol components are not maintained for any significant amount of time. (See Examples 19-22 infra)